1. Field of the Present Disclosure
The present disclosure is directed to a system and method for replacing certain components of a tail drive in an armored face conveyor that may be operated as part of a mechanized longwall mining operation.
2. Related Art
Longwall mining is a form of coal mining that involves removing a long slice of a wall of coal at substantially the same time. The slice may be, for example, from about 0.5 m to 2 m, depending on the longwall mining equipment.
Longwall mining equipment typically includes a shearer (or power loader), an armored face conveyor (AFC), and a plurality of hydraulic jacks, which are commonly referred to as powered roof supports, shields or chocks. The shearer comprises a main body, a housing that holds the electrical components, and a plurality of tractive motive units to move the shearer along a coalface. The shearer may weigh about 75-120 tons. The machine may further include one or more hydraulic pumping units. At either end of the main body of the shearer are fitted ranging arms, which can be ranged vertically up or down by means of hydraulic rams, and onto which are mounted shearer cutting drums that may be fitted with about 30-60 cutting picks. Within the ranging arms may be housed very powerful electric motors (e.g., typically up to 850 kW) which transfer their power through a series of lay gears within the body the arms to the drum mounting locations at the extreme ends of the ranging arms where the cutting drums are. The cutting drums may rotate at a speed of about 20-50 revs/min to cut the mineral from coal seam.
Modern mechanized longwall mining operations may use one or more shearers to remove coal from the face of a coal seam to a depth of, for example, about 0.5 to 2 meters. The coalface may be hundreds of meters wide, and the coal seam may have a depth of hundreds or thousands of meters. The shearer(s) may move along the length of the face carried on the AFC.
The AFC may include a chainless haulage system that resembles, for example, a rugged rack and pinion system specially developed for mining. The shearer typically moves on the AFC at a speed of about 0 to 30 m per minute, depending on cutting conditions. The AFC may be placed in front of the powered roof supports and configured to capture and remove the coal cut by the shearing action of the rotating drums cutting into the coal seam. The AFC may further include a scraper chain conveyor that carries the cut coal to a main gate, where it is loaded onto a network conveyor for transport to the surface, outside of the coal mine. At the main gate, the coal is typically reduced in size, for example, by a crusher, and loaded onto a conveyor by, for example, a beam stage loader.
Each of the hydraulic jacks may be about 1.75 m wide and extendable to a cutting height of up to about 6 meters. The hydraulic jacks may be placed in a long line, side-by-side for up to about 400 meters in length in order to support the roof of a coalface. An individual jack may weigh about 30-40 tons and have a yield rating of about 600-1250 tons. The hydraulic jacks may hydraulically advance about 1 meter at a time.
During mining, a shearer moves along the AFC, cutting coal from a wall as it travels along the AFC, which is removed from the cutting area to create a cavity. The powered roof supports move forward into the newly created cavity. As mining progresses and the entire longwall mining apparatus progresses through the seam, the goaf increases. This goaf may collapse under the weight of the overlying strata. In some situations, the strata may be approximately 2.5 times the thickness of the coal seam removed and may collapse with the beds above settling onto the collapsed goaf.
Additional equipment may be located at the head of the longwall mining apparatus. This equipment, which may be housed in a unit known as the “head gate” or “main gate,” typically includes the primary drive for the AFC, which is known as the “head drive” or “main drive.” Similarly, equipment may be housed at the tail of the longwall, in the tail gate. The tail gate may include an auxiliary or “tail drive” for the AFC.
The AFC itself may be made of a series of line segments. Each segment may have a flat pan and contoured sidewalls. The sidewall may have a groove or contour above the pan and a second groove or contour below the pan, giving it a cross-section similar to an upper case Greek letter sigma. Flight bars, with their ends contoured to slide within the grooves of the sidewall, may be pulled along the upper surface of the pan by chains. Coal may be pulled along the AFC by the flights bars and delivered to the main gate. From the main gate, the flight bars may travel to the tail gate and tail drive by sliding along the grooves located underneath the pan.
While this system is efficient, it is subject to a great deal of mechanical and frictional stresses during normal operations. When there is a failure anywhere within the longwall mining apparatus, the entire operation must be shut down while a replacement or repair is effected. For example, a failure of a component within the tail drive of the AFC will result in a shut down of the entire longwall mining operation, so that the malfunctioning unit can be repaired separately from the other components of the mining operation. Because longwall mining is such an efficient method, downtime may result in the loss of hundreds or thousands dollars in revenue each minute.
In general, in the tail drive of an AFC, the bottom of the spool (or sprocket) may be aligned with the pans, resulting in the top of the spool being higher than the pans. In this implementation, the flight bars and chains must travel from the top of the spool down to the pans. A top sigma directs the flight bars down to the pans. In so doing, the flight bars contact the underside of the top sigma, resulting in tremendous wear on the sigma in this section. The friction caused by the vertical movement of the flight bars on the underside of the top sigma may be great and may result in the sigma being one of the more frequently repaired components of an AFC. When the wear becomes too great, the entire longwall mining apparatus must be shutdown while the sigma is repaired or replaced.
Accordingly, there is a need for effecting replacement of damaged or malfunctioning parts that minimizes downtime for the mining operation.